Polymeric films have been traditionally used to provide barrier properties in limited use or disposable items. The terms "limited use" and "disposable" mean that the product or component is used only once, or only a small number of times, before being discarded. Examples of such products include, but are not limited to, surgical and health care related products such as hospital drapes and gowns, disposable work wear such as coveralls and lab coats and personal care absorbent articles such as diapers, training pants, incontinence products, sanitary napkins, bandages, wipes and the like. In the area of protective apparel, films are used to prevent cross-exchange of microorganisms between the patient and the wearer. Films are used as the outer covers in personal care absorbent articles to prevent body wastes from contaminating the clothing, bedding and other aspects of the surrounding environment.
Lamination of films has been used to create materials that are impervious. Surgical gowns and the outer covers of premium-priced diapers are some examples. A primary purpose of the film in such laminations is to provide barrier properties. The laminates must also be tough, i.e., have high tensile strength in both the machine direction and the cross machine direction, for durability.
Vapor permeable, liquid impermeable polymeric films are also known in the art. One method of making a polymeric film vapor permeable, includes mixing a matrix polymer with a substantial quantity (e.g., 10-70% by weight) of an organic or inorganic particulate filler such as, for example, calcium carbonate, and extruding a film from the blend. The matrix polymer may include a polyolefin, for instance polypropylene or polyethylene, various olefin copolymers, and/or polymer blends. The film may be a monolayer film, a multilayer film which contains the filled layer as a primary layer, or a multilayer film having more than one filled layer.
Then, the film is heated and stretched, causing voids to form in the areas surrounding the filler particles. The voided film is characterized by thin polymer membranes and/or fine pore networks which permit the molecular diffusion of water vapor through the film, but which block the passage of liquids. In essence, a tortuous path is created from one film surface to the other which permits transfer of vapors but not liquids.
Breathable films are also used in surgical apparel. In the past, primary objectives have been to provide good water vapor transmission and make the gowns comfortable to the wearers. The film itself provides good vapor permeability and some liquid barrier, but often has low strength. The film can be laminated to one or more polymeric nonwoven webs to provide a laminate having good strength. Yet some of today's medical applications require surgical apparel which has increased barrier to liquids such as blood, and viruses (often contained in blood), when exposed to a liquid insult which may be under pressure. This objective requires a film that is liquid-impermeable, virus-impermeable, and strong.